I think in most cases the drive, where the files should be recovered, will be attached as a second drive (at least). So from a system point of view there should not be that many changes. You could create something like an expert mode, where the user needs to know what he is doing. In this mode you can save the list, and continue working with it. And since you are in expert mode, you are doing it at your own risk. It means you really should know what you are going to do. In the best case Recuva could install a device driver, which makes sure that no clusters are being overwritten by another process. If there are no free clusters, the device driver should report the drive as 100% full.